This invention relates to barrier coatings providing oil and grease resistance to paper and paperboard substrates. More particularly this invention relates to recyclable, FDA compliant coatings having oil and grease resistant properties and products prepared by application of such coatings to paper and paperboard substrates. When applied to the paper and paperboard, the coated product constitutes a recyclable FDA compliant product that can be used as a food contact surface.
Fluorochemical free barrier coatings are disclosed for providing oil and grease resistance to paper and paperboard, to bags, wrappings and containers prepared therefrom particularly such products used in contact with food. The barrier coatings of the invention operate to absorb the oil and/or grease and to provide a tortuous path to their migration through the coating so as to reduce or eliminate their penetration into the paper or paperboard substrate onto which they have been applied.
Accordingly, the present invention provides non-fluorochemically treated coatings for reducing and perhaps eliminating the migration of oil and/or grease originating from food products wrapped or packaged in films, containers, boxes and the like, into the paper or paperboard substrate onto which they have been applied.
Fluorochemicals are perceived as toxic and a health hazard and in some instances are additionally objectionable because they create odor or flavor changes in the food product.
It is known in the art of paperboard manufacture to apply coatings to the surface of paperboard for various reasons. For instance, U.S. Pat. No. 4,421,825, discloses the application of a coating comprising titanium dioxide and an acrylic copolymer to paperboard to minimize browning of the paperboard at temperatures up to about 205 degree C. It is also known in the art to apply barriers to the paperboard surface, particularly the food contact surface of the paperboard, to satisfy FDA requirements for safe packaging. In most instances the treatment of the paperboard or like sheet material is to prevent or inhibit the migration of contaminants from the paperboard into the packaged food stuffs (see U.S. Pat. No. 5,153,061). These barriers usually take the form of polymer coatings which have achieved FDA clearance for food contact or they may be in the form of a layer of aluminum foil laminated to the paperboard surface. Polyethylene (LDPE, HDPE, LLDPE), ethylene vinyl alcohol copolymers (EVOH), polyvinlyidene chloride (PVDC), nylon, and polyethylene terephthalate (PET) coatings are examples of such barriers. Nevertheless, such barrier materials are not applied to every packaging situation, particularly where it is desired to provide oil and grease resistance to the container by substantially eliminating oil and grease migration from the packaged foodstuffs at the coating applied onto the paperboard substrate.
In order to be effective, coatings as contemplated herein must constitute flexible films capable of resistance to penetration by oil and or grease. In addition, it is critical that these properties remain intact after the paper has been converted from a flat sheet into a label, bag or package. This is because folding the sheet can create pinholes and cracks which can reduce or eliminate any grease barrier in the coating. Synthetic polymers such as styrene acrylic latex, polyvinyl alcohol, polyvinyl acetate and a natural polymer such as starch are primarily responsible for imparting these characteristics to the coating. These polymers form crosslinkable films capable of providing barrier properties. The synthetic polymers also provide hydrophobicity. Starch is typically a more brittle film than latex and is hydrophilic. Consequently, it can crack when folded. However, by modifying its molecular weight and molecular weight distribution, a starch film can be made more flexible without losing its barrier properties.
In order to counteract the tendency of mitration, absorbing or tortuous barrier coatings can be applied to the surface of the paper or paperboard. The coatings of the absorbent type perform as a sink to absorb the oil or grease while the tortuous barrier type coatings act to provide a tortuous path for the migration of the oil or grease. Both effects can be realzied by applying a coating containing both types of materials, generally pigments.
The choice of pigments used is dependent in part on the final product desired and the type of coating equipment available for use.
It is accordingly an object of the present invention to provide a means for reducing and perhaps eliminating the migration of oil and grease from food products packed in paper or paperboard package containers and bags by applying barrier coatings to the paper or paperboard used in forming the containers or bags and the like prepared therefrom.